Expand and fix widget library

[KernAttila]

Describe the enhancement
Some basic widgets are missing from the library :

• int slider
• float slider

Some options could be added to CueLabelLineEdit:

• file browser
• folder browser
• make it read only

And some fixes:

• CueSelectPulldown is not properly fed previous selected options
• CueSelectPulldown does not stretch to get available space
• CueLabelToggle has no default value

Readability can be improved:

• No hover css on CueSelectPulldown
• CueSelectPulldown list has no borders, making it blend with the background.

Screenshots
File browser with filters:

Folder Browser:

Int/Float sliders:

CueSelectPulldown stretch:

CueSelectPulldown hover css:

Read-only CueLabelLineEdit:

Version Number
0.22